Fan case abradable

ABSTRACT

A fan case and method of manufacturing a fan case, for a gas turbine engine, where the fan case has a hollow tubular metal shell with: a central axis of symmetry; an inlet; an outlet; and peripheral wall about the axis to encompass the tips of a plurality of rotary fan blades, and the shell wall includes an upstream portion defining an annular abradable material recess that extends axially having an upstream end at the shell inlet and a downstream end located upstream from the shell outlet.

TECHNICAL FIELD

The invention relates to a fan case for a gas turbine engine havingabradable material.

BACKGROUND OF THE ART

Typically, fan cases are constructed of a metal shell with abradablematerial encapsulated or bounded by metal surfaces within a recessmachined into the metal shell surface. Since the abradable material isrelatively soft and fragile, placing the abradable material in therecess between upstream and downstream walls of relatively tough andresilient metal of the shell provides protection. However, this approachis costly in time, labour, and material use, and there is room forimprovement.

Features that distinguish the present invention from the background artwill be apparent from review of the disclosure, drawings and descriptionof the invention presented below.

DISCLOSURE OF THE INVENTION

The invention provides a fan case, for a gas turbine engine, where thefan case has a hollow tubular metal shell with: a central axis ofsymmetry; an inlet; an outlet; and peripheral wall about the axis toencompass the tips of a plurality of rotary fan blades, and the shellwall includes an upstream portion defining an annular abradable materialrecess that extends axially having an upstream end at the shell inletand a downstream end located upstream from the shell outlet.

The invention also provides a method of manufacturing a fan casecomprising the steps of: fabricating a hollow tubular metal shellhaving: a central axis of symmetry; an inlet; an outlet; and peripheralwall about the axis to encompass the tips of a plurality of rotary fanblades, the shell wall including an upstream portion defining an annularabradable material recess that extends axially having an upstream end atthe shell inlet and a downstream end located upstream from the shelloutlet; and filling the recess with abradable material filling saidrecess and defining an upstream edge of unsupported abradable materialradially inward of the shell inlet.

DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily understood, one embodiment ofthe invention is illustrated by way of example in the accompanyingdrawings.

FIG. 1 is an axial cross-sectional view through a prior art gas turbineengine, showing the various components that are assembled to produce anengine, and an example of a prior art fan case with an encapsulatedlayer of abradable material.

FIG. 2 is a detailed axial cross-sectional view through another exampleof a prior art fan case with an encapsulated layer of abradable materialhaving metal to metal contact in an upstream portion with abradablematerial recess downstream.

FIG. 4 is a detailed sectional view of the embodiment shown in FIG. 3.

FIG. 5 is an exploded isometric view of the metal fan case shell boundedby front and rear flanges, and showing abradable material tiles removedfrom the recess in which they are bonded.

FIG. 6 is a like isometric view of the metal fan case shell showingabradable material tiles installed in the recess.

Further details of the invention and its advantages will be apparentfrom the detailed description included below.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an axial cross-section through a turbo-fan gas turbineengine. It will be understood however that the invention is equallyapplicable to any type of engine with a combustor and turbine sectionsuch as a turbo-shaft, a turbo-prop, or auxiliary power units. Airintake into the engine passes over fan blades 1 in a fan case 2 and isthen split into an outer annular flow through the bypass duct 3 and aninner flow through the low-pressure axial compressor 4 and high-pressurecentrifugal compressor 5. Compressed air exits the compressor 5 througha diffuser 6 and is contained within a plenum 7 that surrounds thecombustor 8. Fuel is supplied to the combustor 8 through fuel tubes 9which is mixed with air from the plenum 7 when sprayed through nozzlesinto the combustor 8 as a fuel air mixture that is ignited. A portion ofthe compressed air within the plenum 7 is admitted into the combustor 8through orifices in the side walls to create a cooling air curtain alongthe combustor walls or is used for cooling to eventually mix with thehot gases from the combustor and pass over the nozzle guide vane 10 andturbines 11 before exiting the tail of the engine as exhaust.

The prior art fan case 2 shown in FIG. 1 has a recessed portion adjacentthe tips of the fan blades 1 that includes an encapsulated layer ofabradable material 12 and some designs include other impact absorbentmaterials such as ballistic fabric or mesh and metal honeycombstructures. The recess to house the abradable material in the prior artis radially outward of the front flange 13 and the fan case 2 is boltedto the engine with the rear flange 14. Due to the geometry of therecess, the fan case 2 is generally fabricated by machining the recessfrom an oversized casting and abradable material 12 is plasma spraycoated into the recess.

FIG. 2 shows another example of a prior art fan case 2 with an enclosedlayer of abradable material 12. The upstream tip of the blade 1 is inmetal to metal contact with a circumferentially grooved portion of thefan case shell 15 and the blade tips contact the abradable material 12housed in the recess downstream. Metal of the fan case shell 15 axiallybounds or encapsulates the relatively softer abradable material 12upstream and downstream in this prior art example as well.

FIG. 3 shows an axial cross-section through the fan case 2 according tothe invention with the fan case 2 being fabricated with a hollow tubularmetal shell 15 having a central axis 16 of symmetry; an inlet surroundedby the front flange 13; an outlet surrounded by the rear flange 14; andperipheral metal wall 17 about the axis 16 to encompass the tips of therotary fan blades 1.

As better seen in the detail of FIG. 4, the shell wall 17 includes anupstream portion defining an annular abradable material recess 18. Therecess 18 fully extends axially from it's upstream end at the shellinlet 19 surrounded by the front flange 13 to the downstream end 21located upstream from the shell outlet 20 surrounded by the rear flange14.

The shell inlet 19 has an inlet diameter and the recess has a recessdiameter that is no greater than the inlet diameter. Compared to theprior art examples shown in FIGS. 1-2, the prior art examples showrecess diameters greater than the inlet diameters and hence theabradable material is axially bounded by the metal of the fan case shell15 in the prior art.

The recess diameter shown in the embodiment of FIGS. 3-4 is tapered in adownstream direction having a maximum recess diameter at the upstreamend of the recess 18 that is equal to the shell inlet diameter and aminimum recess diameter at the downstream end 21 of the recess 18. Theabradable material 12 partially or fully fills the recess and anupstream edge 22 of unsupported abradable material 12 radially inward ofthe shell inlet 19.

The shell 15 includes a front flange 13 at the inlet 19 to which aninlet cowl is bolted and a rear flange 14 at the outlet 20 to bolt thefan case 2 to the engine. Of advantage in manufacturing, the frontflange 13 has an external diameter greater than an external diameter ofthe rear flange 14 as illustrated with a dashed line parallel to theaxis 16. This feature enables access to use simple metal formingtechniques and reduces the need to use relatively expensive metalforging and machining methods of the prior art. Fabricating the hollowtubular metal shell 15 can be accomplished with less expensive metalfabrication procedures such as: press forming sheet metal; welding;rolling sheet metal; and spin forming and need not follow the prior artmethods of forging the metal shell 15 as a single oversized forging andthen machining to remove excess metal material.

As best seen in FIGS. 5-6 the metal fan case shell 15 may be fabricatedwith the forwardly open recess 18 and prefabricated molded abradabletiles 23 can slide into the recess 18 to be bonded to the metal shell 15thereby filling the recess 18. In the embodiment illustrated there arefour tiles 23 each covering one quarter of the circumference of therecess 18, however various other tile patterns can be used. The axialseam between the tiles 23 may be filled and bonded together to fill theentire recess 18. The molded abradable tiles 23 also have a moldedupstream edge 22 of unsupported abradable material 12 that is disposedradially inward of the shell inlet on installation.

As a result of using prefabricated molded tiles 23 costs may be reducedand a greater variety of materials can be used for the abradable layer12. Molding of the tiles 23 frees the choice of abradable materials frommaterials that can be powdered and plasma spray coated to materials thatcan be molded and then bonded to metal.

Although the use of a particular abradable tile is described andpreferred, any suitable abradable provided in any suitable format may beused with the present method and/or apparatus.

Recapping the process of manufacturing a fan case 2 in accordance withthe invention, the following steps are involved. A hollow tubular metalshell 15 is fabricated having: a central axis of symmetry 16; an inlet19; an outlet 20; and peripheral wall 17 about the axis 16 to encompassthe tips of a plurality of rotary fan blades 1. The metal shell wall 17includes an upstream portion defining an annular abradable materialrecess 18 that extends axially from the upstream end at the shell inlet19 to the downstream end 21 located upstream from the shell outlet 20.The recess 18 is filled with abradable material 12 leaving an upstreamedge 22 of unsupported abradable material 12 radially inward of themetal shell inlet 19.

Since the abradable material 12 can slide into the recess 18 as shown inFIGS. 5-6, the step of filling the recess 18 can include moldingprefabricated abradable material tiles 23 apart from the metal shell 15and then bonding the tiles 23 into the recess 18 formed in the shell 15.

Although the above description relates to a specific preferredembodiment as presently contemplated by the inventors, it will beunderstood that the invention in its broad aspect includes mechanicaland functional equivalents of the elements described herein.

1. A fan case, for a gas turbine engine, comprising: a hollow tubularmetal shell having: a central axis of symmetry; an inlet; an outlet; andperipheral wall about the axis to encompass the tips of a plurality ofrotary fan blades, wherein: the shell wall includes an upstream portiondefining an annular abradable material recess that extends axiallyhaving an upstream end at the shell inlet and a downstream end locatedupstream from the shell outlet.
 2. A fan case according to claim 1wherein the shell inlet has an inlet diameter and wherein the recess hasa recess diameter that is no greater than the inlet diameter.
 3. A fancase according to claim 2 wherein the recess diameter is tapered in adownstream direction having a maximum recess diameter at the upstreamend that is equal to the inlet diameter and a minimum recess diameter atthe downstream end of the recess.
 4. A fan case according to claim 1including abradable material filling said recess and defining anupstream edge of unsupported abradable material radially inward of theshell inlet.
 5. A fan case according to claim 1 wherein the shellincludes a front flange at the inlet and a rear flange at the outlet,and wherein the front flange has an external diameter greater than anexternal diameter of the rear flange.
 6. A fan case according to claim 1including molded abradable tiles bonded to the shell and filling therecess.
 7. A fan case according to claim 6 wherein the molded abradabletiles have a molded upstream edge of unsupported abradable material thatis disposed radially inward of the shell inlet on installation.
 8. Amethod of manufacturing a fan case comprising the steps of: fabricatinga hollow tubular metal shell having: a central axis of symmetry; aninlet; an outlet; and peripheral wall about the axis to encompass thetips of a plurality of rotary fan blades, the shell wall including anupstream portion defining an annular abradable material recess thatextends axially having an upstream end at the shell inlet and adownstream end located upstream from the shell outlet; and filling therecess with abradable material filling said recess and defining anupstream edge of unsupported abradable material radially inward of theshell inlet.
 9. A method of manufacturing according to claim 8 whereinthe step of filling the recess includes: molding prefabricated abradablematerial tiles apart from the shell; and bonding said tiles to therecess in the shell.
 10. A method of manufacturing according to claim 9wherein the prefabricated abradable material tiles are molded with anupstream edge of unsupported abradable material for installationradially inward of the shell inlet.
 11. A method of manufacturingaccording to claim 8 wherein the step of fabricating the hollow tubularmetal shell consists of metal fabrication procedures selected from thegroup consisting of: pressing forming sheet metal; welding; rollingsheet metal; spin forming.
 12. A method of manufacturing according toclaim 8 wherein the step of fabricating the hollow tubular metal shelldoes not include forging the metal shell as a single oversized forgingand then machining to remove excess metal material.